Channeled communication systems include systems such as selective call radio communication systems, cable distribution systems, and infrared communication systems. Some selective call radio communication systems, such as paging systems, are multichannel systems in which differing types of information are transmitted on different channels within a transmission band. An example of such a system is a paging system in which one or more information service channels are used to distribute information from information services and one or more messaging channels are used to distribute normal paging messages generated by a variety of originators. Information services provide information such as stock market quotations and scores of sporting events. Some paging subscribers in such a paging system have a desire to simultaneously receive both paging messages intended for the subscriber and some portion of the information available on one of the information service channels. While it is theoretically possible to organize the paging messages and the portion of the information that the subscriber desires so that the subscriber obtains both by using a conventional receiver that switches between two channels, in practice it is very difficult to organize the messages and information in two channels, in systems having any but the fewest number of users. From a subscriber's perspective, this situation can lead to lost information and delayed paging messages, and from the system operator's perspective, this results in unhappy customers and lost revenue.
A potential solution to this problem is to provide a pager that uses two conventional receivers, allowing simultaneous recovery of the information service information and the paging messages, but this approach has drawbacks. When two conventional single channel superheterodyne receivers are used in one pager, local oscillator signals generated in each receiver can interfere with the operation of the other receiver, particularly at certain combinations of channel frequencies. The interference is likely to be severe enough to prevent the receivers from maintaining a locked tuning condition. Furthermore, two antennas would be used, greatly increasing the size of the two channel pager.
Thus, what is needed is a dual channel receiver for use in a communication system that is economical in both size and cost, and that works with all combinations of channels within a band.